fix(receipts): bound canonical document complexity

[AetherAI3]

Summary

• make receipt integer acceptance deterministic at 640 significant decimal digits
• enforce an iterative 64-container nesting limit independent of Python recursion settings
• validate Unicode object keys without invoking hostile repr implementations
• map canonicalization failures consistently through Watchdog replay and CLI diagnostics
• publish package 1.0.8 while retaining receipt v1, Watchdog v1, and IR 0.1.0/1.0.0

Evidence

• independent merge-entry review GREEN
• focused receipt/Watchdog: 167 passed
• full: 994 passed, 2 skipped
• contribution checker: 53 ready
• +/-640 accepted, 641 path-aware ReceiptError; depth64 accepted, 65 rejected with recursionlimit 66
• retained in-domain canonical bytes unchanged, including all pre-release goldens
• clean archive wheel 1.0.8 with 120/120 assets and catalog 53
• four golden changes are identity.nanoVersion 1.0.7 to 1.0.8 only

No global interpreter mutation, receipt/Watchdog/IR version change, ambient I/O, or performance claim.